#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <sys/reboot.h>
#include <sys/types.h>
#include <sys/wait.h>

#define DEV_PATH "/dev/power"
#define BUFFER_SIZE 2

void execute_command(const char *cmd) {
    pid_t pid = fork();
    if (pid == -1) {
        perror("fork failed");
        return;
    }
    
    if (pid == 0) {
        execl("/bin/sh", "sh", "-c", cmd, NULL);
        perror("execl failed");
        exit(EXIT_FAILURE);
    } else {
        int status;
        waitpid(pid, &status, 0);
    }
}

void reboot_system() {
    printf("reboot command received, system rebooting...\n");
    sync();
    execute_command("reboot");
}

void shutdown_system() {
    printf("shutdown command received, system shutting down...\n");
    sync();
    execute_command("shutdown -hP now");
}

int main() {
    int fd;
    char buf[BUFFER_SIZE];
    ssize_t nread;
    
    fd = open(DEV_PATH, O_RDONLY);
    if (fd == -1) {
        fprintf(stderr, "cannot open device node %s: %s\n", 
                DEV_PATH, strerror(errno));
        fprintf(stderr, "please ensure:\n");
        fprintf(stderr, "1. device node /dev/power exists\n");
        fprintf(stderr, "2. sufficient permissions to access\n");
        fprintf(stderr, "3. kernel driver is loaded\n");
        return EXIT_FAILURE;
    }
    
    printf("monitoring %s, waiting for commands...\n", DEV_PATH);
    printf("'r' -> reboot system\n");
    printf("'p' -> graceful shutdown\n");
    printf("press Ctrl+C to exit\n\n");
    
    while (1) {
        nread = read(fd, buf, sizeof(buf) - 1);
        
        if (nread == -1) {
            if (errno == EINTR) {
                continue;
            }
            perror("read device node failed");
            break;
        } else if (nread == 0) {
            printf("device node closed, exiting\n");
            break;
        }
        
        buf[nread] = '\0';
        
        for (int i = 0; i < nread; i++) {
            char ch = buf[i];
            
            switch (ch) {
                case 'r':
                case 'R':
                    printf("detected character '%c'\n", ch);
                    reboot_system();
                    break;
                    
                case 'p':
                case 'P':
                    printf("detected character '%c'\n", ch);
                    shutdown_system();
                    break;
                    
                default:
                    printf("unknown character: '%c' (ASCII: %d)\n", ch, ch);
                    break;
            }
        }
    }
    
    close(fd);
    return EXIT_SUCCESS;
}